The enhanced physical downlink control channel (ePDCCH) is a important physical layer control channel in the Long Term Evolution (LTE) system of 3rd Generation Partnership Project (3GPP), it is mainly used to bear downlink control information (DCI), and the DCI includes resource allocations and other control information on one or more user equipments (UE). In LTE, uplink and downlink resource scheduling information (e.g., information, such as modulation code scheme (MCS) and resource allocation (RA), etc.), are all born by the PDCCH. Generally, the UE firstly needs to demodulate the DCI in the PDCCH, and then demodulates the physical downlink shared channel (PDSCH) (it includes a broadcast message, paging, and data of the UE, etc.) that belongs to the UE itself in the corresponding resource location. Due to the importance of the DCI, when the ePDCCH is used to transmit the DCI, a more robust modulation scheme is typically adopted, such as quaternary phase shift keying (QPSK), and the like.
Currently, the 3GPP LTE system supports multiple DCI formats, the following gives a brief introduction of DCI formats supported by 3GPP LTE Release-8 (R8):
DCI 0: used for PUSCH scheduling.
DCI 1: used to schedule one PDSCH codeword.
DCI 1A: used for compression scheduling of one PDSCH codeword and the random access process initiated by one command.
DCI 1B: used for compression scheduling of one PDSCH codeword with precoding information.
DCI 1C: used for high compression scheduling of one PDSCH codeword.
DCI 1D: used for compression scheduling of one PDSCH codeword with precoding information and power offset information.
DCI 2: used to schedule one PDSCH codeword under the situation of closed-loop spatial multiplexing.
DCI 2A: used to schedule one PDSCH codeword under the situation of open-loop spatial multiplexing.
DCI 3: used to transfer the transmit power control (TPC) command of the physical uplink control channel (PUCCH) and the physical uplink shared channel (PUSCH), and power adjustment information of 2 bits is used.
DCI 3A: used to transfer the TPC command of the PUCCH and PUSCH, and power adjustment information of 1 bit is used.
Wherein, the information bit fields mainly included in the DCI are as follows: a PUSCH frequency hopping flag, PUSCH resource allocation and frequency hopping allocation, an MCS level, a redundancy version (RV), a new data indicator (NDI), a TPC command for the scheduled PUSCH, cyclic shift and an orthogonal cover code (OCC) index for the demodulation reference signal (DMRS), an uplink (UL) index, a downlink assignment index (DAI), a channel state information (CSI) request, a sounding reference signal (SRS) request, a resource allocation type, a hybrid automatic repeat request (HARQ) procedure number, a TPC command for the scheduled PUCCH, etc.
With the evolution of the LTE technology, the 3GPP LTE can support more and more functions. Accordingly, new control information transmitted by the ePDCCH are more and more, e.g., for the time division duplexing (TDD) mode of the 3GPP LTE, uplink/downlink subframe configuration information of the TDD is semi-statically configured in the early release of the LTE, but if the network can use a related control channel to dynamically transmit the uplink/downlink subframe configuration information to a terminal user, it has a great significance for the system making full use of the features for the dynamic change of the uplink and downlink services and the dynamic change of the interference in the system to achieve the maximization of capacity. For aspects of using the ePDCCH to transmit the new control information, there are some methods in the related art below:
In method 1, reserved bits in related control format are used.
For example, some reserved bits are typically in the DCI 0, and these bits can be used to represent certain information. For example, the reserved bits are used to trigger the UE to perform the transmitting of the measurement reference signals aperiodically, etc.
In method 2, a new DCI is designed, for example, to support the precoding of which the rank is 1, some bits are added to indicate the precoding information, based on the DCI 1A, thereby forming a new DCI 1D.
However, both methods have great limitations, which present that:
For method 1, since the reserved bits are generally fewer, there are generally only 1-2 bits for the control information that can be transmitted. Moreover, if the reserved bits are used for transmitting certain information, when the new information is transmitted in the future, the method cannot be used any more. And, not all the control formats have the reserved bits.
For method 2, it will significantly increase the complexity of the receiver detecting the control channel, however, in the 3GPP LTE system, the location of the PDCCH transmitted by the transmitter is uncertain, the receiver needs to perform blind detections in multiple possible resource locations to determine if there is a DCI transmitted to itself according to the work mode of the receiver and the features of different control information formats. Adding a new control format will cause the detection complexity of the receiver to be increased dramatically, while introducing the new DCI will also bring relatively large control channel overhead.
For the 3GPP LTE system, beside using the ePDCCH to transmit the control information, the physical control format indicator channel (PCFICH) and the physical broadcast channel (PBCH) are also used to transmit the control information, and the PCFICH carries information of 2 bites to indicate the number of the orthogonal frequency-division multiplexing (OFDM) symbols occupied by the PDCCH control channel in the subframe where the PCFICH is located. The PBCH carries system bandwidth, system frame number information, automatic retransmission resource configuration information, etc., and the PBCH and PCFICH adopt QPSK modulation, which is the same as ePDCCH. And the differences are that, the formats of the PCFICH and PBCH are fixed, and the transmitted resource locations are fixed, and in the related art, there is no method for using the PCFICH, PBCH to carry the new control information.